Conventional hybrid electric vehicles (or “HEVs”) include thermal devices to control the vehicle cabin temperature for passenger comfort. When the engine is warmed the engine coolant can add thermal energy to the vehicle's heating, ventilation and air conditioning system (or “HVAC”). Existing HEV controls are configured to enable the coolant temperature to quickly reach and maintain a desired range. Sunload is typically not accounted for in these strategies. When there is full sunload, the electronic automatic temperature control system (or “EATC”) does not need the discharge air to be as warm as it would be without any sunload. For example, in some vehicles the necessary target discharge air temperature can be around 15° F. to 20° F. lower than it would be in a no sun condition. Consequently, engine coolant temperature targets are calibrated to be higher than they need to be in sunnier conditions. Current EATC systems control the discharge air temperature by moving a blend door to blend in cooler air. Since the engine coolant is warmer than needed for heating purposes, the discharge air is remedially cooled down through blending in cool air. Therefore, energy is being wasted by heating the engine coolant more than what is necessary.
One existing cooling system for a hybrid electric vehicle is taught in U.S. Pat. No. 6,450,275 titled “Power Electronics Cooling for a Hybrid Electric Vehicle.” The '275 patent teachings determining speed for a cooling fan based upon the electronic components of the vehicle and the internal combustion engine. It is desirable to have a vehicle thermal management system that accounts for sunload.
Another existing HVAC takes a number of variables, including sunload, into consideration in controlling the vehicle interior temperature. See U.S. Pat. No. 5,988,517 titled “Method and System for Controlling an Automotive HVAC System Based on the Principle of HVAC Work.” Still this system does not consider control of the vehicle's powertrain to accommodate the vehicle's climate needs.
Therefore, there is a need for a method of controlling an HEV's thermal management system in consideration of solar energy. Unnecessary powering on and off of the engine or vehicle powertrain can be avoided.